Soundcheck Browsers

Soundcheck runs in Chrome by default. With --browser firefox or --browser webkit it checks the site in Firefox or in WebKit (Safari's engine) instead, to catch what breaks in only one browser. This page covers picking an engine, what runs in each and how comparisons handle them. For Chrome itself (the download, the sandbox), see the FAQ.

rhythm soundcheck snapshot staging.yoursite.com --name ff --browser firefox
# …make your change…
rhythm soundcheck compare

--browser

Value	Uses
chrome (default), chromium	an installed Chrome or Chromium, else the downloaded Chrome for Testing
firefox	an installed Firefox: firefox, firefox-esr, firefox-developer-edition or firefox-nightly on PATH, or /Applications/Firefox.app on macOS
webkit, safari	a WebKit driver: WebKitWebDriver or WPEWebDriver (Linux) or safaridriver (macOS)
a path, e.g. /usr/bin/google-chrome	that Chrome binary
firefox=<path>, webkit=<path>	that engine's binary

Engine names ignore case. Soundcheck downloads only Chrome; Firefox and WebKit must be installed. A typo stops before the run, exit 2:

rhythm soundcheck: --browser: "firefx" isn't chrome, firefox or webkit (did you mean firefox?)

Without the engine installed, the run stops with exit 3:

rhythm soundcheck: no WebKit driver found; install WebKitWebDriver (Linux) or enable safaridriver (macOS), or pass the path to it

For Firefox the message is no Firefox found; install it or pass the path to its binary. On macOS, turn safaridriver on once with safaridriver --enable.

What runs in Firefox and WebKit

Firefox runs headless in a throwaway profile and is driven through WebDriver BiDi. Health, visual, cache and exec run as in Chrome. The modules that work inside the page through Chrome's DevTools protocol are skipped, each with a note:

Snapshot "ff" saved; all clear - 0 errors, 0 warnings, 1 notice - 4 pages · 9s
note: speed was skipped in firefox: it needs Chrome
note: interact was skipped in firefox: it needs Chrome

Module	Chrome	Firefox	WebKit
health	yes	yes	yes; with a classic-only driver, no console, network or status facts
visual	yes	yes	yes; with a classic-only driver, viewport-only screenshots
cache	yes	yes	yes
exec	yes	yes	yes
interact (and so echo, which records what form submits send)	yes	skipped	skipped
speed	yes	skipped	skipped
a11y, seo	yes	skipped	skipped
logging in	yes	skipped (the login was skipped in firefox: logging in needs Chrome)	skipped

Other differences you may see:

• Network errors keep the engine's words: NS_ERROR_CONNECTION_REFUSED where Chrome says net::ERR_CONNECTION_REFUSED.
• The phone pass outside Chrome only sets the 390 x 844 window size, with no phone emulation, so Not responsive can't fire there.
• Chrome's own console messages (CSP and mixed-content warnings from the browser) have no Firefox counterpart.
• WebKit drivers that offer only classic WebDriver can't send -H, --cookie or --user-agent to the site alone, so each page fails with not supported by this browser rather than sending them everywhere.

Screenshots of another engine are stored as shots/<page>-<viewport>-<engine>.png.

Comparing

compare runs in the snapshot's engine unless you pass --browser, as it does for modules, levels and viewports. The settings line names it:

Settings: from snapshot "ff" (modules health,visual,cache; levels inspect,click; viewports desktop,mobile; browser firefox)

A comparison in Firefox reads like one in Chrome:

[BROKE] Page not found (404) - /about.php
  fix: Restore the page, or redirect it and update links to it.
[NEW] Broken link to /about.php (404) - /, /contact.php, /shop.php
  fix: Update or remove the link, or redirect the old URL.
[NEW] PHP Warning: Undefined array key "layout" - /, /contact.php, /shop.php
  source: themes/acme/footer.php:42
  fix: Fix the code at the source line and turn display_errors off in production so visitors never see these.
[NEW] JS error: Uncaught ReferenceError: undefinedStoreLocator is not defined - /
  source: inline script
  fix: Open the browser console on this page to see the full stack.

Passing another engine than the snapshot's is a change you made, listed with the others (You changed: modules health,visual,cache -> health (--modules); browser firefox -> chrome (--browser)). Screenshots and speed only compare within one engine, so the comparison warns browser engines differ (snapshot firefox, now chrome); screenshots and speed only compare in the same engine. With --strict it stops instead:

rhythm soundcheck: --strict: this comparison wouldn't use snapshot "ff"'s settings: browser firefox -> chrome (--browser)

To cover more than one browser, keep a snapshot per engine and compare each:

rhythm soundcheck snapshot staging.yoursite.com --name chrome
rhythm soundcheck snapshot staging.yoursite.com --name ff --browser firefox
# …make your change…
rhythm soundcheck compare --snapshot chrome
rhythm soundcheck compare --snapshot ff

In a fleet, a site's args may name an engine (--browser firefox) but never a path.

---

_{← Import from BackstopJS and Lost Pixel · Home · CLI reference →}